This invention relates to preloading rail clips and insulators into steel railway sleepers.
Steel railway sleepers have been widely used for many years and are usually either formed from strip steel or rolled at the steel mill with an appropriate cross section. The steel thickness is usually in the range of 6-12 mm. Shoulders are attached to the sleeper to provide abutments to locate the rails so that the correct rail gauge width can be maintained. Usually these shoulders also serve as mountings for fasteners which hold the rail down. The fasteners may be ordinary bolts or resilient spring clips.
Many different means have been used to fix the shoulders in place. These include bolts and nuts, welding, deforming the top of the sleeper to form a rail abutment for use with clips which fit in pierced holes in the top sleeper surface, and shoulders which hook into holes in the top sleeper surface. However, in actual track use there have been many problems such as nuts continually coming loose, sleeper cracking around the edges of shoulder welds, sleeper cracking adjacent to deformed abutments which create locally stiff regions, and sleeper cracking from the edges of holes pierced in high stress areas.
One of the most successful methods of attaching the shoulder is where the shoulder hooks into a round hole near the lateral centre of the sleeper top where the stresses are relatively low. The highest stresses are near the lateral edges of the sleeper top where the stiffness is greatest. In shoulders of this type, projecting below the shoulder top there is a generally circular stem having a hook and a spur extending from the bottom of it. In use, the hook extends towards the rail and the spur extends away from the rail.
The hook type fastening as described is prior art and generally works well. However, it has one major disadvantage in that clips cannot be preloaded in the shoulders in a parking position prior to the rail being installed.
An important issue for railways is the reduction of labour costs associated with laying new track and replacing rails in existing track.
One way of obtaining significant labour cost reductions is to preload the clips, insulators, and rail pads into the new sleepers at the sleeper manufacturing plant so that when the sleepers are placed in track it is only necessary to drop the rail in place and mechanically push the rail clips into their final position.
This feature of preloading clips is known for concrete sleepers, but it is not possible for hook-in shoulders for steel sleepers because the shoulders are not actually locked in the sleeper until the rail and insulators are in place. Consequently, there is a good chance that if it was attempted to press the clips in place without the rail in position, the shoulder would come out of the hole in the sleeper. Even if it were possible to pre-install the clips in the shoulders, the shoulders could still bounce out of the holes from the impact of shunting and other shocks received while on the rail trucks en route to the track installation site.
Pre-loading costs much less than distributing the pads, insulators and clips along the track then manually placing the components in place and introducing the clips into the shoulders by hand. Obviously, this is not an efficient process and in addition the labour costs are high because of lost time in moving workers to and from the moving work site plus the limited track access times.
At the sleeper plant it is possible to largely mechanise the preloading of the components since it is a fixed and easily controlled environment.
Accordingly, it is desirable to allow clips, insulators and shoulders to be preloaded into a steel sleeper, and to be retained there during transport to the desired site for track work.
According to one aspect of the present invention there is provided a preloaded sleeper assembly including a steel railway sleeper having two shoulder mounting openings for each rail, and associated with each mounting opening, in combination, a shoulder including a hook and a spur inserted through the opening and located in an operative position, an insulator located on said shoulder on the side near the intended rail position, and a rail clip mounted on said shoulder;
characterised in that the said insulator includes a member which extends into the mounting opening so as to lie between the walls of said opening and said shoulder and thereby prevent movement of the shoulder towards the intended rail position, the rail clip being mounted on said shoulder in a parking position, so that the shoulders, insulators and clips are retained on said sleeper.
Thus, an embodiment of the present invention provides a new mounting arrangement, in which the insulator includes a projection or spigot extending into the opening in the sleeper.
This projection serves to prevent relative movement of the sleeper and shoulder, so that in transit the shoulder, insulator and clip assembly does not come loose from the sleeper. This enables a preloaded sleeper to be prepared, which can then be placed on the intended track ready for the rail to be fixed. This provides a considerable saving in labour over earlier proposals.
Preferably, the opening in the sleeper is circular or oval in shape.
Preferably, the shape of the member of the insulator is such as to substantially fill the cavity in the opening caused by the difference in size between the opening and the part of the shoulder passing through the opening.
In a preferred embodiment, the insulator is retained on the shoulder by means of a pair of recesses for receiving a corresponding pair of flanges or wings on said shoulder.
According to a further aspect of the present invention there is provided a method for preloading a steel railway sleeper with shoulders, rail clips and insulators, said sleeper including two shoulder mounting openings for each rail, said shoulder including a hook and spur, said method including the steps of:
a) inserting said shoulder into said opening and rotating it, so that the hook lies toward the intended rail position and the spur away from it;
b) locating said insulator onto the shoulder on the side near the intended rail position, said insulator including a projection which extends into the mounting opening so as to prevent movement of the shoulder towards the intended rail position;
c) driving said rail clip into a preload parking position, such that the shoulder, insulator and clip are retained on said sleeper.
Preferably, the step of locating the insulator onto the shoulder includes sliding the insulator over a pair of flanges on the shoulder, to be slidably received in corresponding recesses in the insulator.
The insulator may be retained in its located position by the preloaded and parked clip engaging the insulator in that position.